1. Field of the Invention
The present invention relates to the manufacturing of semiconductor devices. More particularly, the present invention relates to an apparatus for baking wafers.
This is a counterpart of Korean Patent Application No. 2001-4585, filed Jan. 31, 2001, the contents of which are incorporated herein by reference in their entirety.
2. Description of the Related Art
Spin-coating equipment for use in photolithography typically include apparatus for baking a spin-coated wafer. In general, such an apparatus performs various baking processes such as pre-bake and post-bake processes.
Referring to FIG. 1A and FIG. 1B, an apparatus 10 for baking wafers generally comprises a chamber, a heating plate 12 disposed in the chamber for supporting a wafer 30 thereon, and a lifting device (not shown) having lifting pins for loading and unloading the wafer 30 onto and from the heating plate 12. The lifting pins of the lifting device extend through the heating plate 12 and are movable up and down relative to the heating plate 12. Thus, after the wafer 30 is loaded onto the lifting pins by a robot, the lifting pins can be lowered until the wafer 30 is placed on the upper surface of the heating plate 12.
However, the upper surface of the heating plate 12 is sometimes slightly inclined. In such a case, the wafer 30 can slide along the upper surface of the heating plate 12 as the lifting pins are being lowered. A guide 14 comprising a plurality of guide pins is disposed along the periphery of the heating plate 12 to prevent the wafer 30 from sliding off of the heating plate 12 as it is being placed thereon.
However, the guide 14 may present another problem in connection with the positioning of the wafer 30 on the heating plate 12. For example, an error can be made in setting the robot to transfer the wafer to the desired position or the robot itself may experience a mechanical error. When either of these errors occur, the wafer 30 can be incorrectly placed on the heating plate 12, i.e., a portion of the wafer 30 can be set atop one of the guide pins of the guide 14 as shown in FIG. 1B. As a result, the wafer 30 will not be heated evenly during the bake process. Consequently, the thickness of the resulting photo-resist (TPR) will vary beyond the design tolerance or the critical dimension (CD) of the wafer will vary. In the worst case, a pattern bridge will form on the wafer or a portion of the wafer designated to be patterned will not in fact be patterned.
Thus, the improper placement of the wafer on the heating plate 12 can lead to serious defects in the wafer 30. Up until now, such defects have only been uncovered as the result of a check of the production rate or an inspection that is made after the overall manufacturing process is completed. That is, production processes are continuously carried out on a wafer before it is discovered that a defect was produced in the wafer as the result of the improper placing of the wafer on the heating plate. Obviously, fabricating wafers of inferior quality before the cause of a defect in the wafers is uncovered lowers the production rate.
Accordingly, an object of the present invention is to provide an improved apparatus for baking a wafer, which apparatus can prevent a defect from being formed on the wafer as the result of an incorrect placement of the wafer on the heating plate of the apparatus, thereby ensuring that quality semiconductor devices are manufactured from the wafer and contributing to the productivity of the manufacturing process.
To achieve this object, the present invention provides an apparatus for baking a wafer, which apparatus can detect whether the wafer is situated correctly on the heating plate.
The apparatus for baking a wafer according to the present invention includes the heating plate on which the wafer is to be supported horizontally during the baking process, a lifting device associated with the heating plate for loading and unloading the wafer onto and from the heating plate, and means for detecting whether the wafer loaded onto the heating plate by the lifting device extends parallel to the upper surface of the heating plate.
The detecting means includes at least two proximity sensors spaced at uniform intervals from one another in or on the heating plate. The proximity sensors sense the respective distances from the locations thereof to the wafer and generate signals representative of the sensed distances. The detecting means also includes a controller for determining whether the wafer is situated correctly on the heating plate and hence, whether a manufacturing process should be carried out, on the basis of the signals generated by the proximity sensors. The controller is also connected to the working elements of the apparatus, e.g. the heater, to control the manufacturing process.
In the present invention, the proximity sensors are mounted, respectively, in grooves in the upper surface of the heating plate. Preferably, the entirety of each proximity sensor, with the exception of a sensing surface thereof, is disposed within the heating plate beneath a respective groove in the upper surface of the plate. The sensing surface is exposed within the groove and becomes the only exposed surface of the sensor. Specifically, the sensing surface is preferably disposed 0.5 mm from the upper surface of the heating plate. The grooves can be disposed along lines that emanate from the center of the heating plate and subtend equal angles of 120 degrees.
Also, the controller can generate an alarm in the form of a sound or a visual alarm message when at least one of the proximity sensors fails to produce a signal indicating that the wafer is disposed no further than a predetermined distance therefrom.